Methods of bonding solder balls to bond pads on a substrate

ABSTRACT

Methods and apparatuses for bonding solder balls to bond pads are described. In one embodiment, portions of a plurality of solder balls are placed within a frame and in registered alignment with individual bond pads over a substrate. While the ball portions are within the frame, the balls are exposed to bonding conditions effective to bond the balls with their associated bond pads. In another embodiment, a frame is provided having a plurality of holes sized to receive individual solder balls. Individual balls are delivered into the holes from over the frame. The balls are placed into registered alignment with a plurality of individual bond pads over a substrate while the balls are in the holes. The balls are bonded with the individual associated bond pads. In another embodiment, a frame is provided having a hole. A solder ball is provided having an outer surface. The solder ball is retained within the hole in an ambient processing environment which is generally uniform over the entirety of the ball&#39;s outer surface. While the solder ball is within the hole, the solder ball is bonded with an associated bond pad on a substrate.

TECHNICAL FIELD

The present invention relates to methods of bonding solder balls to bondpads on a substrate, and to bonding frames.

BACKGROUND OF THE INVENTION

As integrated circuitry becomes smaller and more dense, needs ariserelative to the packaging and interconnecting of fabricated integratedcircuitry devices. Concerns associated with increasing the speed withwhich integrated circuitry devices are packaged and the efficiency withwhich the devices are packaged drive the industry to find faster andmore flexible systems and methods for packaging integrated circuitry.Specifically, one aspect of integrated circuitry packaging includesbonding conductive balls or solder balls on bond pads of a substrate forsubsequent connection to packaging structure. Such is commonly referredto as solder ball bumping.

In the formation of solder-bumped substrates, solder ball material isprovided over bond pads of a substrate supporting integrated circuitrythereon. If the substrates are to be flip-chip bonded to anothersubstrate, it is important that the solder balls be of uniform size.Otherwise, some of the balls might not make desirable contact with thebond pads of the substrate to which it is to be bonded. This problem ledto development of pre-formed solder balls which are formed to a specificcommon tolerance dimension such that all of the solder balls areessentially the same size. Hence, when the solder balls are bonded bysolder melting/welding to substrates, each will essentially project fromthe outer substrate surface a common distance and accordingly makecontact with all bond pads when being bonded.

This invention arose out of concerns associated with providing improvedmethods and apparatus for packaging integrated circuitry.

SUMMARY OF THE INVENTION

Methods and apparatus for bonding solder balls to bond pads aredescribed. In one embodiment, portions of a plurality of solder ballsare placed within a frame and in registered alignment with individualbond pads over a substrate. While the ball portions are within theframe, the balls are exposed to bonding conditions effective to bond theballs with their associated bond pads. In another embodiment, a frame isprovided having a plurality of holes sized to receive individual solderballs. Individual balls are delivered into the holes from over theframe. The balls are placed into registered alignment with a pluralityof individual bond pads over a substrate while the balls are in theholes. The balls are bonded with the individual associated bond pads. Inanother embodiment, a frame is provided having a hole. A solder ball isprovided having an outer surface. The solder ball is retained within thehole in an ambient processing environment which is generally uniformover the entirety of the ball's outer surface. While the solder ball iswithin the hole, the solder ball is bonded with an associated bond padon a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a side elevational view of a portion of a frame which isdisposed in a position to receive one or more solder balls in accordancewith one or more embodiments of the present invention.

FIG. 2 is a side elevational view of a portion of a frame which isdisposed in a position to receive one or more solder balls in accordancewith one or more embodiments of the present invention.

FIG. 3 is a side elevational view of a portion of a frame which isdisposed in a position to receive one or more solder balls in accordancewith one or more embodiments of the present invention.

FIG. 4 is a side elevational view of a frame engaged with a substrate inaccordance with one or more embodiments of the invention. A portion ofthe frame has been broken away to show detail.

FIG. 5 is a view of the FIG. 4 frame undergoing processing in accordancewith one embodiment of the invention.

FIG. 6 is a view of the FIG. 4 frame undergoing processing in accordancewith one embodiment of the invention.

FIG. 7 is a view of the FIG. 4 frame and substrate after the solderballs have been bonded with their individual associated bond pads.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Referring to FIG. 1, a portion of a frame in accordance with oneembodiment of the invention is shown generally at 10 and includes anouter surface 12 having at least one, and preferably a plurality ofholes 14 therein. Holes 14 are preferably sized to receive individualsolder balls 16 having individual solder ball outer surfaces 18. In oneembodiment, the frame and holes are dimensioned to permit one and onlyone solder ball to be received within each hole at a time. In apreferred embodiment, a majority portion of an associated solder ball isreceived within each hole.

The solder balls can be provided into frame-supported positions in avariety of ways. In one embodiment, individual solder balls 16 aredelivered into holes 14 from over frame 10, as FIG. 1 implies. Inanother embodiment (FIG. 2) a plurality of solder balls 16 are providedover surface 12, at least some of which being deposited into at leastsome of holes 14. The balls can be provided over the surface in anymanner. In the illustrated example, balls 16 are provided over surface12 by rolling at least one, and preferably a plurality of the balls overthe surface and into individual respective holes 14. The balls can berolled over the frame surface until individual balls drop intoindividual associated holes. Alternately considered, frame 10 positionedin proximity to a substrate (not shown) to which conductive balls are tobe bonded can be dipped into a volume of balls. Thereafter, the frameand substrate are removed from the volume of balls, with individualballs be received in respective frame holes. The balls are preferablysmall enough to pass through the holes.

Referring to FIG. 3, and in accordance with another embodiment of theinvention, more solder balls 16 are provided than there are holes inouter surface 12. In this example, three solder balls 16 are providedfor the two illustrated holes 14. One of the balls and the frame ismoved relative to the other of the balls and the frame effective todeposit a ball into each hole. In this example, balls 16 are moved oversurface 12 effective to deposit one solder ball into each hole. Excesssolder balls, such as the leftmost solder ball 16, which were notdeposited into a hole are removed from over surface 12. Removal ofexcess balls can be effected in any suitable way. Alternatelyconsidered, frame 10 positioned in proximity to a substrate (not shown)to which conductive balls are to be bonded can be dipped into a volumeof balls. Thereafter, the frame and substrate are removed from thevolume of balls, with individual balls being received in respectiveframe holes.

Referring to FIG. 4, frame 10 is shown in proximity with a substrate 20having thereon a plurality of bond pads 22. Holes 14 hold one individualsolder ball respectively, in registered alignment with an associatedbond pad 22 on substrate 20. In one embodiment, each solder ball 16 isplaced on a fluxless bond pad surface. Fluxless bond pad surfaces arepreferably used in this embodiment because the frame maintains eachindividual solder ball in registered alignment with an associated bondpad prior to and during solder ball bonding described below. Thisembodiment can overcome some problems presented through the use of fluxon bond pads. Specifically, flux will typically have to be completelycleaned from a substrate after the bonding process. This embodiment canpermit the post-bonding cleaning step to be eliminated therebysimplifying the bonding process.

This embodiment also permits at least two solder balls 16 to becontemporaneously retained over different respective bond pads onsubstrate 20. In a preferred embodiment, frame 10 is moved to proximatesubstrate 20 before any of the balls are delivered into the holes.Subsequently, individual balls can be provided or delivered into theholes as described above.

In another embodiment, the solder balls are retained within each hole inan ambient processing environment which is generally uniform over theentirety of each ball's outer surface 18. Specifically, while each ballis retained within its associated hole and in registered alignment withan associated bond pad, the processing environment outwardly of eachball is generally uniform. That is, retaining each ball within itsrespective hole can take place without the use of any outsideenvironment-changing conditions such as vacuum pressure and the like ononly a portion of the respective balls. The balls are preferablyinserted into their associated hole from a position within the ambientprocessing environment without separately and discretely providing avacuum force against only portions of each ball during bonding. Suchnon-vacuum retention provides more flexibility and increases thesimplicity with which the balls can be processed.

Once having been placed in proximity with their individual associatedbond pads, the individual solder balls can be bonded with their bondpads. The balls can be bonded separately, or can be bonded all at onceas through suitable heat processing. Such can take place in any suitablemanner, with but two examples being described below in connection withFIGS. 5 and 6.

Referring to FIGS. 5 and 6, solder balls 16 are exposed to bondingconditions effective to bond the balls with their associated bond pads22. In one embodiment, the solder balls are reflowed under such bondingconditions while they are within their individual holes. For example,the two leftmost balls in FIG. 5 and the three rightmost balls in FIG. 6are seen to have been reflowed while within their individual holes. In apreferred embodiment, a laser-bonding system 24 is provided and solderballs 16 are laser-bonded with their associated bond pads.

In one laser-bonding embodiment (FIG. 5), laser bonding is effected byfixing the position of frame 10 and moving a laser beam 26 relative tothe frame from ball-to-ball. In this way, a laser beam is moved relativeto and between individual balls to engage each ball.

In another laser-bonding embodiment (FIG. 6), laser bonding iseffectuated by fixing the position of a laser beam 26 and moving frame10 relative to the laser beam from ball-to-ball. In this example, frame10 is moved in the direction of the arrow immediately below substrate20. Accordingly, the three rightmost solder balls 16 have been reflowedby laser 26 while the four leftmost solder balls remain to be processed.Such comprises moving individual solder balls relative to agenerally-fixed laser beam.

Referring to FIG. 7, frame 10 is moved away from proximity withsubstrate 20. Preferably, frame 10 is moved away from substrate 20 afterindividual solder balls are exposed to the bonding conditions. In thisexample, the holes are preferably dimensioned so that they do not overlyrestrict removal of the frame after the balls are reflowed. Accordingly,such comprises removing individual holes from around their associatedreflowed balls. Of course, the frame could be moved away from thesubstrate prior to the exposure of the balls to the bonding conditions,particularly if flux or some other agent or means is used to retain theballs on their pads during bonding.

In another aspect of the invention, a frame is provided having aplurality of ball-supporting features which maintain at least two ballsin registered alignment with a substrate having bond pads thereon. In apreferred embodiment, the ball-supporting features comprise individualholes which extend through the frame and which are dimensioned toreceive only one ball at a time. The holes are preferably disposed overthe frame in a template-like orientation which matches the orientationof bond pads with which the solder balls are desired to be bonded. Theinventive frames can enable a large number of solder balls to besimultaneously placed into bond pad-engaging positions where they can besubsequently bonded in a time-saving fashion.

Aspects of the invention enable solder balls to be placed with greaterprecision and in greater numbers than was previously possible. Suchenables throughput to be increased and provides for better integratedcircuitry packaging uniformity. In addition, solders balls can be placedand bonded in greater numbers on fluxless bond pads which can increasethroughput by expediting processing.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of bonding balls of solder to bond pads on a substratecomprising: dipping the substrate into a volume of the balls of solder;contemporaneously retaining at least two of the balls of solder overdifferent respective bond pads on the substrate in absence of flux; andwith the at least two balls of solder so retained, exposing the at leasttwo balls of solder to bonding conditions effective to bond the at leasttwo balls of solder with the associated bond pads.
 2. The method ofclaim 1, wherein the exposing comprises laser-bonding the at least twoballs of solder.
 3. The method of claim 1, wherein the exposingcomprises melting the at least two balls.
 4. A method of bonding ballsof solder to bond pads on a substrate comprising: placing at leastportions of a plurality of balls of solder within a frame and inregistered alignment with individual bond pads over the substrate bydipping the substrate into a volume of the balls of solder; and whilethe ball portions are within the frame, exposing the balls of solder tobonding conditions effective to bond the balls of solder with theassociated bond pads.
 5. The method of claim 4, wherein the exposingcomprises laser bonding the balls with the associated bond pads.
 6. Themethod of claim 4, wherein the exposing comprises laser bonding theballs with the associated bond pads by fixing the position of a laserbeam and moving the frame relative to the laser beam from one of theballs to another of the balls.
 7. The method of claim 4, wherein: theplacing comprises placing individual balls within individual holeswithin the frame; and the exposing comprises reflowing the balls whilethe balls are within the individual holes, and further comprising, afterreflowing, removing the frame from around the reflowed balls.
 8. Amethod of bonding balls of solder to bond pads on a substratecomprising: providing a frame having a plurality of holes sized toreceive individual solder balls; delivering the individual balls ofsolder into the holes from over the frame by dipping the substrate intoa volume of the balls of solder; placing the balls into registeredalignment, while the balls are in the holes, with a plurality ofindividual associated bond pads over the substrate; and bonding theballs with the individual associated bond pads.
 9. The method of claim8, wherein the bonding comprises laser bonding the balls with theindividual associated bond pads.
 10. The method of claim 8, wherein thebonding comprises laser bonding the balls with the individual associatedbond pads by fixing a position of a laser beam and moving the framerelative to the laser beam from one of the balls to another of the ballsto effectuate the bonding.
 11. A method of bonding solder balls to bondpads on a substrate comprising: providing a frame having a plurality ofholes; inserting individual solder balls into the holes by dipping thesubstrate into a volume of the balls of solder, the balls being smallenough to pass through the holes; placing the frame into proximity withthe substrate having bond pads positioned thereon, more than one of theplurality of holes individually holding an individual solder balltherewithin and in registered alignment with an associated bond pad onthe substrate; laser-bonding the solder balls to the associated bondpad; and after the laser bonding, removing the frame from proximity withthe substrate.
 12. The method of claim 11, wherein said laser-bondingcomprises moving the individual solder balls relative to agenerally-fixed laser beam.
 13. A method of bonding a ball of solder toa bond pad on a substrate comprising: providing the frame having a hole;providing a ball of solder having an outer surface; retaining the ballof solder within the hole in an ambient processing environment which isgenerally uniform over an entirety of the outer surface of the ball bydipping the substrate into a volume of balls of solder; and while theball of solder is within the hole, bonding the ball of solder with anassociated bond pad on the substrate.
 14. The method of claim 13,wherein the bonding comprises laser bonding the ball.
 15. A method ofbonding balls of solder to bond pads on a substrate comprising:providing a surface having a plurality of holes therein; providing aplurality of balls of solder over the surface by dipping the substrateinto a volume of the balls of solder; depositing some of the balls ofsolder into at least some of the holes; and bonding the balls of solderwhich were deposited into the holes to individual associated bond padspositioned on the substrate proximate the holes.
 16. The method of claim15, wherein the bonding comprises laser-bonding each ball to anassociated one of the individual associated bond pads.
 17. The method ofclaim 15, wherein the bonding comprises laser-bonding each ball to anassociated one of the individual associated bond pads by fixing aposition of a laser beam and moving each ball into a path of the laserbeam.
 18. A method of bonding balls of solder to bond pads on asubstrate comprising: placing at least portions of a plurality of ballsof solder within a frame and in registered alignment with individualbond pads over the substrate by dipping the substrate into a volume ofthe balls of solder; and while portions of the balls of solder arewithin the frame, exposing the balls to bonding conditions effective tobond the balls with the individual bond pads by laser bonding the ballswith the individual bond pads.
 19. The method of claim 18, wherein theexposing the balls to bonding conditions effective to bond the ballscomprises laser bonding the balls with the individual bond pads byfixing a position of a laser beam and moving the frame relative to thelaser beam from one of the balls to another of the balls.
 20. The methodof claim 18, wherein: the placing comprises placing individual ballswithin individual holes within the frame; and the exposing the balls tobonding conditions effective to bond the balls comprises reflowing theballs by laser bonding while the balls are within the individual holes,and further comprising, after reflowing, removing the frame from aroundthe reflowed balls.
 21. A fluxless process for bonding balls of solderto bond pads on a substrate comprising: placing at least portions of aplurality of balls of solder within a frame and in registered alignmentwith individual bond pads over the substrate by dipping the substrateinto a volume of the balls of solder; and while portions of the balls ofsolder are within the frame, laser bonding the balls with the individualbond pads by laser bonding the balls of solder to the individual bondpads using a fixed laser beam.
 22. The fluxless process of claim 21,wherein the laser bonding the balls to the individual bond padscomprises fixing a position of the laser beam and moving the framerelative to the laser beam from one of the balls to another of theballs.
 23. The fluxless process of claim 21, wherein: the placingcomprises placing individual balls of solder within individual holeswithin the frame; and the laser bonding the balls to the individual bondpads comprises reflowing the balls by laser bonding while the balls arewithin the individual holes, and further comprising, after reflowing,removing the frame from around the reflowed balls.